Optical instruments, particularly endoscopes, for medical and non-medical purposes are mainly fluid-tight systems. It remains possible, however, for a series of reasons, that moisture can penetrate the housing, which can lead to a clouding of the optical systems that adversely affects visibility. Problems can occur, for instance, as early as the manufacturing of the instruments in normal atmosphere, if the residual moisture in the atmospheric air is precipitated in the housing interior. In addition, moisture can penetrate because of minor leakiness at joints or seams at which the instrument can be disassembled for purposes of maintenance, repair, or installation. The instruments can suffer additional impacts, for instance with medical endoscopes, from cleaning by means of autoclaving, in which the instrument is exposed to superheated steam at about 140 degrees C. under varying pressure. This temperature impact can result in fine cracks, through which moisture, in turn, can penetrate into the housing.
To avoid such condensation problems from moisture precipitated on the optical system, a familiar method with optical instruments calls for positioning in the housing a hygroscopic substance which binds the moisture occurring inside the housing before it precipitates on the at least one optical system.
Thus, for instance, it is a familiar process to distribute the hygroscopic substance in loose form in the housing. This has the disadvantage, however, that moving the instrument causes noises as well as wearing of the hygroscopic substance, which can settle on the optical systems in the form of dust.
Patent DE 101 13 365 A1 describes an optical instrument. In this instrument the hygroscopic substance is embedded in a shapable matrix material, which can be replaceably inserted into the eyepiece recesses of the instrument. The shapable matrix material thus serves as a support scaffold for the hygroscopic material.
In addition, in DE 195 07 205 A1 it is proposed that the hygroscopic substance should be positioned under a removable wall piece of the housing, which is connected gas-tight with the other housing wall by means of a coupling. This embodiment allows for a rapid, easy replacement of the hygroscopic substance, but with the disadvantage that the endoscope has an additional opening whose fluid-tight quality must be ensured.